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RFC 1423 - 2.2 RSA-MD5 Message Digest Algorithm

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### 2.2 RSA-MD5 Message Digest Algorithm

The RSA-MD5 message digest is computed using the algorithm defined in RFC 1321 [10]. The character string "RSA-MD5" within an encapsulated PEM header field indicates the use of this algorithm. Also, as defined in RFC 1321, the object identifier

         md5 OBJECT IDENTIFIER ::= {
             iso(1) member-body(2) US(840) rsadsi(113549)
             digestAlgorithm(2) 5
         }

identifies this algorithm. When this object identifier is used with the ASN.1 type AlgorithmIdentifier, the parameters component of that type is the ASN.1 type NULL.

The RSA-MD5 message digest algorithm accepts as input a message of any length and produces as output a 16-octet quantity. When symmetric key management is employed, an RSA-MD5 MIC is encrypted by splitting the MIC into two 8-octet halves, independently encrypting each half, and concatenating the results.

When symmetric key management is employed with this MIC algorithm, the symmetrically encrypted MD5 message digest is represented in the fourth argument of a "Key-Info:" header field as a contiguous string of 32 ASCII hexadecimal digits (corresponding to a 128-bit MD5 message digest).

To avoid any potential ambiguity regarding the ordering of the octets of a MD5 message digest that is input as an RSA data value to the RSA encryption process, the following holds true. The first (or left- most displayed, if one thinks in terms of a digest's "print" representation) octet of the digest (i.e., the low-order octet of A as specified in RFC 1321), when considered as an RSA data value, has numerical weight 2**120. The last (or right-most displayed) octet (i.e., the high-order octet of D as specified in RFC 1321) has numerical weight 2**0.

Next: 3. Symmetric Key Management Algorithms

Connected: An Internet Encyclopedia
RFC 1423 - 2.2 RSA-MD5 Message Digest Algorithm